The present invention relates to a medical instrument for dissecting tissue in the human or animal body.
An instrument for dissecting tissue is one used for cutting and for grasping tissue, for example a punch, a pair of scissors or a forceps.
Instruments of this kind are used in the context of minimally invasive surgery for dissecting tissue in the human or animal body, usually under endoscopic monitoring. To this end, instruments of that kind comprise an elongated shaft which has at least one movable tool arranged at its distal end, which usually coacts with another movable or immovable tool, arranged at the distal end of the shaft, for dissecting the tissue. For operating the at least one movable tool, such instruments are further provided, on the proximal end of the shaft, with at least one movable grip element through which the axially movable force transmission element, transmitting thrust and/or pull forces, is non-positively connected with the at least one movable tool so that any movement of the movable grip element is translated by the force transmission element into a movement of the movable tool.
Especially for operations in the region of the ear, nose and throat one normally uses instruments with a shaft having at least one bend in order to permit the tool or tools arranged on the distal end to be advanced to positions that are accessible only with difficulty, for example into niches in the frontal or the maxillary sinus.
An instrument with a bent shaft, especially if the bending radius is small, presents the problem that the force must be transmitted by the force transmission element from the movable grip element through the bend to the movable tool. This is rendered difficult especially in view of the aim to have a slim instrument, i.e. one with a thin shaft.
In order to be able to adapt itself to the bend, the force transmission element must, therefore, be flexible in the region of the bend of the shaft.
DE 44 44 025 A1 discloses, for example, a force transmission element for a medical instrument in the form of a flexible wire element, which is capable of adapting itself to such a bend. However, a flexible wire can transmit only tensile or pull forces, but is not suited for transmitting thrust, or even high thrust. For, if the force transmission element is subjected to thrust, the wire will buckle so that only small, or no thrust can be transmitted to the at least one movable tool for actuating the latter for the purpose of dissecting tissue.
Considering, however, that such instruments are also used for cutting hard tissue, for example cartilage or bone tissue, the nature of the force transmission element must be such to permit even very high forces, especially high thrust forces, to be transmitted to the movable tool without any buckling of the force transmission element, and this, of course, although the transfer of forces must be effected through the bend of the shaft, which means that the force transmission element must be capable of adapting itself to the bending radius during its axial movement.
DE 195 20 717 C2 proposes to solve this problem with the aid of a tubular-shaft instrument with a tubular shaft provided with a bend, where the force transmission element is arranged inside the tubular shaft. In the bent portion of the tubular shaft, the force transmission element is configured as a bar made from a flexible material, which is in contact with the inner wall of a surrounding rigid sleeve, extending concentrically to the shaft, and whose cross-section is reduced, in the region of the bend, by a number of circumferential grooves arranged one beside the other in axial direction. The before-mentioned sleeve may be constituted also by the tubular shaft as such. The circumferential grooves are formed to extend over the full circumference of the bar. Thus, the bar is locally reduced in thickness to sort of a wire with circular cross-section in the region of the circumferential grooves. In the intermediate sections between the grooves, the diameter of the bar is not reduced so that the outer surfaces of the intermediate sections serve as guide surfaces to guide the force transmission element in the region of the bend in contact with the inner wall of the sleeve and/or the tubular shaft.
Although such a force transmission element permits high thrust forces to be transferred through the bend to the movable tool, this known instrument nevertheless must be regarded as disadvantageous with that configuration of the force transmission element.
Considering that such instruments are used in minimally invasive surgery, it is another demand that must be placed on such instruments that their diameter in the region of the shaft be as small as possible to permit the instrument, together with the shaft, to be introduced into an incision or natural opening in the body which should be as small as possible. In the case of such miniaturized instruments with a shaft diameter of a few millimeters only, this means for the known instrument that the force transmission element has an extremely small diameter in the reduced regions of the circumferential grooves, whereby the stability of the force transmission element is reduced because the material thickness of the force transmission element is reduced to very small wire cross-sections in the region of the circumferential grooves. Therefore, the force transmission element may buckle or break in the region of the circumferential grooves extending over the full circumference when high thrust or sudden thrust is transferred, or may fracture when high pull forces are transferred, whereby the operating safety of the known instrument is reduced.
DE 43 00 064 A1 discloses a punch for dissecting tissue having an outer shaft and an inner shaft, at a distal end of which an opening having a blade is provided, which coacts with a counter blade at the distal end of the outer shaft in such a way that, upon actuation of the punch, tissue which protrudes through said opening in the inner shaft, is cut off by the blades moved against each other. The inner shaft is formed rigid, is straight in the proximal region and merges distally into a curved course, and the outer shaft, which forms the force transmission element of this instrument, is at least in the region of this curvature deformable. The deformability of the outer shaft is made possible by that the outer shaft is provided with recesses which face each other on the radius of the curvature of the inner shaft. The recesses in form of radial incisions or notches only leave a narrow bridge of material between themselves.
U.S. Pat. No. 5,507,772 also discloses a medical instrument, the shaft of which comprises a bend. The force transmission element comprises a plurality of notched or recessed sections in the region of the bend of the shaft. Between the recessed sections of the force transmission element a plurality of ribs are formed, the thickness of which substantially conforms to the thickness of the remaining body of the force transmission element. The ribs are formed in direction of one side of the force transmission element only, whereas the force transmission element is configured continuously flat in the region of the bend on the opposite side of the ribs. The force transmission element and the ribs thereof are guided in an elongated slot inside the shaft, which slot is provided in the concave inner side of the bend of the shaft. In another embodiment, the ribs are omitted so that, in this case, the force transmission element is configured in the region of the bend as a flat band, which, however, is not guided in this case.
U.S. Pat. No. 4,646,745 further discloses a medical stapler, which comprises a force transmission element disposed within said shaft, wherein the force transmission element is configured in form of a flat band, so that the force transmission element is flexible. The flat band itself consists of three sheets of thin bands. In the region of a bend of the shaft, the flat band is guided along a spacer element, in order to achieve that the flat band maintains its central position in the shaft in the region of the bend, if the flat band is under tension, i.e. in order to prevent the flat band from becoming straight in the region of the bend of the shaft. The spacer element is provided with ball bearings for reducing the friction between the force transmission element and the space element.
Now, it is the object of the present invention to improve a medical instrument of the before-mentioned kind in such a way that high pull and/or thrust forces can be transferred to the at least one movable tool by means of the force transmission element, through the bend of the shaft, without any buckling of the force transmission element and without any reduction in stability of the force transmission element being encountered in the region of the bend.